A Definitive Example of Aluminum-27 Chemical Shielding Anisotropy

Solid-state²⁷Al NMR spectra have been obtained for a crystalline 1:1 complex of AlCl₃and OPCl₃. Aluminum chloride phosphoryl chloride, AlCl₃· OPCl₃(1), is unusual in that the Al–O–P bond angle is close to 180°. From analysis of the²⁷Al MAS NMR spectra, it was determined that the²⁷Al nuclear quadrupole coupling constant is 6.0(1) MHz, the asymmetry in the electric field gradient (efg) tensor is 0.15(2), and the isotropic chemical shift, δ_iso(²⁷Al), is 88(1) ppm. Solid-state²⁷Al NMR of a stationary sample reveals a line shape affected by a combination of anisotropic chemical shielding and second-order quadrupolar interactions. Analysis of this spectrum yields a chemical shift anisotropy of 60(1) ppm and orientations of the chemical shift and electric field gradient tensors in the molecular frame. Experimental results are compared with those calculated usingab initioHartree–Fock and density functional theory.